Prevention of corrosion in steam generation



Patented Jan. 1, 1952 r PREVENTION OF CORROSION IN STEAM GENERATION Arthur L. Jacoby, Western Springs, 111., assignor I to National Aluminate Corporation, Chicago, 111., a corporation of Delaware No Drawing.

Application June 19, 1947,

Serial No. 755,740

Claims. 1 p

This invention relates to the art of treating water in boilers, steam generators, evaporators' and the like, and the treatment of the steam and the condensate produced therefrom to reduce or prevent the corrosion of steam lines, traps, condensers and other pieces of equipment carrying the steam and the condensate. The .invention also relates to the preparation of new and improved water treating compositions.

It is known that certain amines may be added toboiler water from which they will volatilize with the steam and condense and dissolve in the condensed steam to inhibit corrosion occurring in the condensate lines. These amines'may also be added directly to the steam lines. The amines proposed for this purpose are liquids boiling within the range from 0 degreesC. to 171 degrees'C. at atmospheric pressure. These liquid amines are, in general, highly caustic and present a serious hazard in their handling. Furthermore, they are'quite volatile even under ordinary temperature conditions and the toxicity of their fumes in high concentrations presents a further hazard in .their use. Moreover, the additionof liquids to a boiler or to the steam lines is attended with many mechanical and practical difficulties.

An object of the present invention is to provide a composition for the treatment of boiler water, steam and steam condensates, which composition is in a substantially dry form that is readily soluble or dispersible in water, and from which suitable amines are liberated by the action of alkaline boiler Water.

Another object of the invention isto prepare corrosion inhibiting composition of the type described in the form of briquettes which are gradually and uniformly dissolved in the feed water to a steam boiler, .evaporatoror the like. Other objects will appear hereinafter.

In accomplishing these objects in accordance with the invention it has been found that cor-.- rosion inhibition in steam generatin systems can be obtained by incorporating with the boiler feed water certain crystalline non-hygroscopic water soluble polyamine salts, These polyamine salts are solids which are capable of liberatingthe free amines when added to the feed'waterof a steam boiler containing suificient alkali to decompose the amine salts into free amines at steam generating temperatures. These amine salts canalso be incorporated with other water treating chemicals either by mixing them'together to produce a dry,,free'flowing powder or by briquettingthem with a suitable binder, preferably one which is water soluble. The preferred compositions con:

- 2 sist of the amine salts briquetted with other water treating chemicals, e. g., tannins, lignin sulfonates, sodium sulfite, or the like, by means of binders such as dextrines.

Assuming that the alkali added. to the boiler water is sodium hydroxide, the general reaction which occurs between the amine salt and the alkali with the liberation of the amine may be described by the following equation:

Amine salt+NaOH (boiler water)- Amine(vo1atile) +Na-salt (boiler water) 7 Generally speaking, the quantities of amine salt required for the purpose of the invention are so small that the quantities of alkali employed in the boiler water will be suflicient to react with the amine salt and liberate'the free amine while still maintainin an alkaline condition in the boiler Water. In some cases; however, where the amine salt is made up with an excess of acid or acid salt, it may be "desirable to add larger amounts of alkali to the boiler feed water to compensate for the alkali which is utilized in the reaction with the amine salt.- The quantity of alkali required for this purpose can readily be calculated by any one skilled in the art.

The polyamines which are usefulfor the preparation of amine salts in accordance with the practice of the invention should possess the following properties:

1. The polyamine should distill or volatilize with steam in appreciable quantities in the boiler pressure range of superatmospheric pressures from 5 to 250 pounds per square inch or at higher pressures if such pressures are employed.

2. The polyamine should not cause foaming and carryover.

3. It should'not decompose appreciably under boiler conditions of alkalinity, pH, pressure and temperature.

' 4. The boiling pointof the polyamine should preferably be above degrees C. so that appreciable amounts of the amine are not lost in venting or preheating of the feed water and so most of the amine will be in the liquid phase in the portions of the system handling hot condensate. It should be pointed out that boiling point alone is not the factor which determines the relative volatility of the amine with steam, as

the tendency to form. stable hydrates and other factors also influence this behavior.

5.-The polyamine should not form stable carbonic acid addition products which will not decompose to the amine and carbon dioxide at preheater temperatures.

6. The carbonic acid addition products 01 the 8. The polyamine should preferably be oi a type which forms a protective film on the steam and condensate lines that wii1-inhibit--oxygen corrosion.

9. The polyamine should preferably have such vapor pressure characteristics that in b5'iling' di lute aqu ous solutions little change "occurs ji n; the water to amine ratio thus providing nearly constant alkalinity in the boilingwaiterandthe steam condensate.

Specific illustrations of suitable aminesflor most steam systems are ethylenediamiife (bf'p. 1 6 ldeg rees c i an ;diet hy1enetriamine Y (b. ,p. 20? i':r Z- h :w e ini ll ortions: "'Th'e'pmyamme sauseuninera .ganic c anboxylic and/or s'u'lionicfacicl's carfbe prepare-abs di's'solvingthe acid-in 'asol vent, e; a ater, diethyl 'etherjormethanol;an'daddingfthe equivalent quantitypifpolyamine with stirring at a rate s'uchas 't davoid' overheating; ifCooling may be resorted"'toi'iifsomecases."The s'a'lt is h n r cev d bxfil re o a l l if :nss evanoration. In cases .where the corresponding amide is water insoluble care must be taken in the preparation of the salt 'to'avoid dehydration to the amide." Another way' in which'the polyamine' salts"may be conveniently prepared consists" in conducting the' nutralizationlor partial neutralization of thepolyamine'in the pres.- ence' of' a'solid material capebleiof absorbing the water o'frea'ction;'therebv iyieldinga dryadevaporation. An example of this procedure 'isito mix the'polyami'ne' with-a large'iexcess of sodium acid sulfate either witli'orvwithoutrthe additior'i of anhydroussodium' sulfatei" The amine will then be converted tdamiXediamine salt, namely, sodium"amin'sulfate, and th'e water will-b; absorbed by the'excess of salt orFsalts ehetriar'nine as the neutra salts: j

n. The 'mixed alkalimetal' ami e neutral alts of, ethylenediamine monosodium orthophosph'a'te, and the mixed neutralsalts; of ethylenediamine lignin sulforlic acidjand 'sulfuricfacid." I The above mentioned amine saltsar'e s'ubst'ah tially non-hygroscopic solid water soluble "salts, but it will be under stogd that notallbolyaiiklihe 'saltshave s'atis'factory'properties for the purpose of the inventio;n even though the amine 'its'elf ara" "may be suitable in other respects for inhibiting corrosion in a steam system. Thus, the "phnyl acetate of ethylenediamine was too hygroscopic to be isolated.

The following examples are given to show methods of preparing polyamine salts suitable for the practice of the invention and also to i1- Tus'trate" the fiireparatifin 'ibf 'ebiiipo'sitiiins con- *taining such salts, it being understoodyhowever,

that these examples are not intended to limit the scope of the invention.

A fjEmample I Ten (10) parts by weight of diethylenetri- "'an'iineand w partsby weight of nitre cake were lthoroughlym-ixedgin a putty chaser type of mixer until-dilly 'slightly'damp. Upon standing a short 7 time thieslightlydamp mass further reacted to {become dry, whereupon it was ground to give a powder,,, readily water soluble, and containing 10%"*a'n'iine in the form of the sodium and diethylenetriamine mixed sulfate.

- IIr-a putty chaser- 35 partsby weight ofrthe monohydrate om monosodium orthophosphate and 5 partsby weight; of diethylenetriamina were thoroughly mixed after which' 10- parts Oil di gitrinand about 1 part of water-(parts by weight) were added and the 'mixture'br-iquetted. The'briquettes were dry and non-stickm andreadilydis; solved in water.- The aminesalt-formedmasthe sodium and diethylenetriaminemixed phosphate i izl ll' I1] 17,;- W In a putty chaserrZyi parts of monohydrate of monosodium orthophosphate, 11 .5 parts amass nitre cake and 7:5 parts-i of -diethylenetriamine were-thoroughly mixed.- afterwhich 5 parts de'x'ltrin and-2 partslwater were.-added-and;the mifiture briquetted The resulting briquettes-were very hard and-dry --and readilyj=waterf soluble. The amine salts were aunixture "of the-salts which occurin Examples I-and II. J .r 1a..)

E 'campleIV' Y rt;

Fifty (50) parts of mo nehydrate'of ino'r'ibs jdium orthophosphate,' 24;parts of sediummisufite, and l5fparts of! diethylenetriamine were mixed afterwhich '1 parts cf dextrin'an'd '4 parts of water were added and'the mixture brlqlitt'ed. The amine salt formed was mainly the sodium and diethylenetriamine mixedphosphate. Inthe following examples, V.to VII, inclusive, the procedure of mixing was substantiallyihe same as in the Examples ,1 toIV, inclusive; The materials shown were vmadeinto .briquettes a ct p'rdlitithaving the" mndwingariamis f Per cent Sulfate of ethylenediamine 45.5 Sulfonate of the diamine 4.6 Total $0: content 6.1 Lignin organic matter; 42.9

This neutral salt materiaLwas then used in a steam system to inhibit steam corrosion.

As previously stated, in order to introduce the amine salt into the steam system it is preferable to prepare it in the form of a briquette with other water treating chemicals and to cause it"to be dissolved uniformly and gradually by-the feed water to the boiler. This is conveniently'accomplished by preparing the briquette and introducing it into a by-p-ass feeder whichis connected in the boiler'feed water line. The boiler feed water circulates through the feeder gradually dissolving the briquette and carrying the amine salt into the boiler where the amine is liberated by the action of the heat and inorganic alkali present. The liberated amine is then preferably volatilized at a uniform rate such that little change occurs in the water to amine ratio. The manner in which the amine volatilizes will, of course, depend upon the chemical and physical characteristics of the amine. The volatilized amine should serve to provide a nearly constant alkalinity in the boiling water and should redissolve in the steam condensate to provide the desired alkalinity in the latter at the point where condensation occurs.

The quantity of the amine salt initially added to the water from which the steam is generated should preferably be approximately 0.015 pound for each neutralizing amino group per grain of methyl orange alkalinity per thousand gallons of water. This means that if the methyl orange alkalinity of the feed water were the quantity of amine salt would be that quantity capable of liberating 0.15 pound of said amine per thousand gallons of feed water. If the methyl orange alkalinity were 20 the recommended dosage of amine salt would be the equivalent of 0.30 pound.

of said amine per thousand gallons of water. In 1 a similar manner the dosage can be calculated for Waters of different alkalinities. These dosages are based upon a pressure of 250 p. s. i. and the corresponding steam temperatures with ade- 'quate venting of the preheater.

The dosage can also be established by observation of the pH obtained in the condensate. In general, it is preferable to maintain a pH in the steam condensate of about 7.0, although it has been observed that substantial corrosion protection has been obtained at a lower pH, as low as 6.3. The preferred pH range in the steam condensate is about 6.5 to about 7.5.

The treatment described herein can be employed in steam generation where the steam generators are operated at operating pressures from a high vacuum to rather high superatmospheric pressures. It will be understood, however, that of the amines suggested some would be better than others for different pressure operations.

Having thus described the invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. In a process of generating steam, the method which comprises generating steam from an alkaline boiler water while incorporating into the feed. water to the boiler a quantity of a polyamine salt from the group consisting of the neutral hydrochloride, hydrobromide, nitrate, orthophosphate, pyrophosphate, acetate, and Z-naphmixed alkali metal amine neutral salts of ethylenediamine monosodium orthophosphate, the mixed neutral salts of ethylenediamine lignin sulfonic acid and sulfuric acid, the nitrate, the

sulfate, the orthophosphate, the hydrochloride,

the acetate, the phenyl acetate and the 2-naphthalene sulfonate of diethylenetriamine as the neutral salts, the quantity of alkali in the alkaline boiler water being in excess of the'amount required to hydrolyze said salt and the quantity of the salt being effective to liberate a corrosioninhibiting quantity of the polyamine upon said hydrolysis and being equivalent to approximately 0.015 pound for each neutralizing amino group in the amine per grain of methyl orange alkalinity per thousand gallons of water.

2. In a process of generating steam, the method which comprises generating steam from an alkaline boiler water while incorporating into the feed water to the boiler a quantity of a polyamine salt from the group consisting of the neutral hydrochloride, hydrobromide, nitrate, orthophosphate, pyrophosphate, acetate, and 2-naphthalene sulfonate of ethylenediamine, the acid nitrate and acid oxalate of ethylenediamine, the mixed alkali metal amine neutral salts of ethylenediamine monosodium orthophosphate, the mixed neutral salts of ethylenediamine lignin sulfonic acid and sulfuric acid, the nitrate, the sulfate, the orthophosphate, the hydrochloride, the acetate, the phenyl acetate and the 2-naphthalene sulfonate of diethylenetriamine as the neutral salts, the quantity of alkali in the alkaline boiler .vater being in excess of the amount required to hydrolyze said salt and the quantity of the salt being efiective to liberate a corrosion inhibiting quantity of the polyamine upon said hydrolysis and to maintain a pH in the condensate of at least 6.3.

3. In a process of generating steam, the method which comprises generating steam from an alkaline boiler water while incorporating into the feed Water to the boiler a quantity of a polyamine salt from the group consisting of the neutral hydrochloride, hydrobromide, nitrate, orthophosphate, pyrophosphate, acetate, and 2-naphthalene sulfonate of ethylenediamine, the acid nitrate and acid oxalate of ethylenediamine, the mixed alkali metal amine neutral salts of ethyl enediamine monosodium orthophosphate, the mixed neutral salts of ethylenediamine lignin sulfonic acid and sulfuric acid, the nitrate, the sulfate, the orthophosphate, the hydrochloride, the acetate, the phenyl acetate and the Z-naphthalene sulfonate of diethylenetriamine as the neutral salts, the quantity of alkali in the alkaline boiler water being in excess of the amount required to hydrolyze said salt and the quantity of the salt being effective to liberate a corrosion inhibiting quantity of the polyamine upon said hydrolysis and to produce a pH in the steam condensate Within the range of about 6.5 to about 7.5.

4. In a process of generating steam and of condensing the steam so as to protect against corrosion metal parts of the system where the steam is condensed, the method which comprises incorporating into boiler feed water from which the steamis generated and which contains an alkali, a quantity of a neutral sulfate of diethylenetriamine, the quantity of alkali in said boiler water being in excess of the amount required to hydrolyze said sulfate to free the diethylenetri- 8 fzimineimrtheiiquafitity o1: saidfifil llfflteifbelng 513130411159 9. pH in the steam condensate of at efl'ectivextto 1iheratee.:;corrosion inhibiting quan- I1eastfi.3.. A 't r r.

mymn diethylenetriamine and to produce a pH -7- e. e-AR'I'HURYLM-JAGQB. inthesteam condensate of atleast 6.3. W N MW.,, v 2' f- E IIi9-TpIOGeSSi1jOf generating steam and of 55 :1 .m t.- .WB!EEEBE CE$ E r o hdensmg flthe steam jSO .Las fprotect against The following references are of reord ih ,eorro'sion metalsparts of, :the: system where the me ofthi's V .4; r;-

steam is; condensed, the method whichcomprises incorporating vintov boiler :feed water fromwhich i STATES I gtheasteam is generated andwhichcontains an @150 Number; W1; Name n Date .11.: valkalgeaquantity; of a neutral phosphate of di- 2,053,024.. vDreyfus Sept. 1, 1936 ethylenetniamine, -the quantity of alkali in said 2,200,184. ,Morgan May 7;;1940 boi1er =wate1tbeing in excess of the amount re- 2,220,950 Bird Nov. 12,1940

guired to hydrolyze said phosphate to free-the 2,460,259 1 Kahler Jan.25;1949 vg1 i 2tI-1y 1 e1;1etriamjne and-v the quantity of said zm 1 HER =;phospha.te being efiective to liberate a. corrosion e a v a 7 1 tinhjbiting quantity of 'diethylenetriamine and to ZZN u t 35 3 5- 

1. IN A PROCESS OF GENERATING STEAM, THE METHOD WHICH COMPRISES GENERATING STEAM FROM AN ALKALINE BOILER WATER WHILE INCORPORATING INTO THE FEED WATER TO THE BOILER A QUANTITY OF A POLYAMINE SALT FROM THE GROUP CONSISTING OF THE NEUTRAL HYDROCHLORIDE, HYDROBROMIDE, NITRATE, ORTHOPHOSPHATE, PYROSPHOPHATE, ACETATE, AND 2-NAPHTHALENE SULFONATE OF ETHYLENEDIAMINE, THE ACID NITRATE AND ACID OXALATE OF ETHYLENEDIAMINE THE MIXED ALKALI METAL AMINE NEUTRAL SALTS OF ETHYLENEDIAMINE MONOSODIUM ORTHOPHOSPHATE, THE MIXED NEUTRAL SALTS OF ETHYLENEDIAMINE LIGINN SULFONIC ACID AND SULFURIC ACID, THE NITRATE, THE SULFATE, THE ORTHOPHOSPHATE, THE HYDROCHLORIDE, THE ACETATE, THE PHENYL ACETATE AND THE 2-NAPHTHALENE SULFONATE OF DIETHYLENETRIAMINE AS THE NEUTRAL SALTS, THE QUANTITY OF ALKALI IN THE ALKALINE BOILER WATER BEING IN EXCESS OF THE AMOUNT REQUIRED TO HYDROLYZE SAID SALT AND THE QUANTITY OF THE SALT BEING EFFECTIVE TO LIBERATE A CORROSION INHIBITING QUANTITY OF THE POLYAMINE UPON SAID HYDROLYSIS AND BEING EQUIVALENT TO APPROXIMATELY 0.015 POUND FOR EACH NEUTRALIZING AMINO GROUP IN THE AMINE PER GRAIN OF METHYL ORANGE ALKALINITY PER THOUSAND GALLONS OF WATER. 